Healthcare providers are frequently faced with the problem of diagnosing and treating patients suffering from varying levels of pain. The appropriate assessment of a patient's pain is a prerequisite to successful diagnosis and treatment of the pain. However, healthcare providers often have difficulty in making such assessments due to patients' inability to accurately describe the pain that they are experiencing. Those difficulties sometimes result in ineffective, inadequate, and/or excessive treatments.
In more detail, the experience of pain has at least two components: 1) a “sensory”, or nociceptive, component, and 2) an “affective”, or emotional, component. The sensory component comprises the sensory modality of nociception experienced within the somatosensory system in response to certain stimuli, such as nerve fibers carrying information regarding the stimuli to the patient's brain. The affective component comprises feelings of unpleasantness and other emotions associated with the future implications related to pain, such as annoyance, fear, or distress.
Traditionally, healthcare providers have used varying apparatus/methods for subjectively, qualitatively, and/or semi-quantitatively measuring the amount and/or intensity of pain that a patient is suffering. The predominant apparatus/methods that have been used are categorical pain descriptors. For example, FIG. 1A illustrates a verbal pain intensity scale that is used to measure pain intensity based on adjective descriptors (e.g., “no pain”, “mild pain”, “moderate pain”, “severe pain”, “very severe pain”, and “worst pain possible”); FIG. 1B illustrates a numerical pain intensity scale that is used to measure pain intensity based on a numerical rating (i.e., 0 for “no pain” up to 10 for “worst pain possible”); FIG. 1C illustrates a visual analog scale (VAS) that is used to measure pain intensity based on a position along a continuous line between two endpoints (i.e., the closer to the left end point the closer to “no pain” and the closer to the right end point the closer to “worst pain possible”); FIG. 1D illustrates a Wong-Baker pain intensity scale that is used to measure pain intensity based on a face that best represents how the patient is feeling (e.g., a face with the largest smile for “no hurt” and a face that is crying for “hurts worst”); FIG. 1E illustrates a premature infant pain profile (PIPP) pain assessment scale that is used to measure pain based on a score that corresponds to a specific behavioral observation (i.e., a “relaxed body posture” corresponds to “no apparent pain” and “thrashing” corresponds to “severe pain”); and FIG. 1F illustrates a crying, requires oxygen, increased vital signs, expression, and sleepless (CRIES) pain assessment scale that is used to measure pain based on a score that is totaled from a plurality of different behavioral observations (i.e., a “normal” breathing corresponds to a score of 0 and “facial grimacing” corresponds to a score of 2). As those figures illustrate, categorical pain descriptors can be verbal, numerical, visual, observational, or a combination thereof.
The verbal pain intensity scale of FIG. 1A, the numerical pain intensity scale of FIG. 1B, and the VAS of FIG. 1C are generally used in assessing pain intensity in cognitive adults. Those apparatus/methods require a patient to comprehend a physician's or practitioner's questions regarding their pain and to be able to convey, verbally or by otherwise indicating, where they believe their pain falls on each scale to allow for some diagnostic evaluation. The healthcare provider asks the patient to describe his or her pain using corresponding categorical descriptors and then marks the appropriate portion of the scale according to the response.
Those methods cannot be used in patients who cannot convey the intensity or location of their pain to a physician or practitioner (e.g., patient's unable to comprehend their pain or a physician's queries, “non-verbal” patients or otherwise verbally or cognitively challenged patients, patients with developmental disabilities, etc.). Accordingly, the Wong-Baker pain intensity scale of FIG. 1D is used to measure pain intensity in children and cognitively impaired adults. And the PIPP pain assessment scale of FIG. 1E and the CRIES pain assessment scale of FIG. 1F are generally used to measure pain intensity in infants and non-verbal patients. Those two apparatus/methods rely solely on the healthcare provider's observations.
Other apparatus/methods for pain assessment suffer from similar shortcomings. For example, pain tolerance threshold (PTT) and pain perception threshold (PPT) determinations both rely of verbal response from a patient. Those determinations are subjective and semi-quantitative and use electrical stimulation to directly excite both large and small diameter sensory nerve fibers. The PPT determination represents the minimum amount of a potentially noxious electrical stimulus that can be perceived, while the PTT determination represents the maximum amount of noxious electrical stimulus that can be tolerated when used as a clinical diagnostic tool. Thus, PTT determinations are not only dependent on a patient's subjective verbal responses, they also require the patient to experience some amount of aversive stimulus, which not only causes the patient undesirable discomfort, it also elicits the emotional component of pain.
Similarly, the apparatus/methods available for diagnosing neuropathic pain require patient self reporting on the intensity of his or her pain and of its characteristics (e.g., burning, lancinating, throbbing, etc.). That requirement demands a certain level of sophistication and cognitive abilities that is lacking in patients with developmental delay, who are nonverbal, or who are very young. Moreover, it requires the patient's subjective input to execute the testing paradigm.
By virtue of the categorical limitations inherent in the conventional apparatus/methods illustrated discussed above, a healthcare provider inevitably encounters varying descriptions of the same levels of pain intensity from patient to patient, particularly in view of the highly subjective nature of the emotional component of pain. Different people can have different pain thresholds, and those pain thresholds can vary based on outside influences, such as distractions and mood. Those contextual and cognitive factors are partly the result of the fact that pain most often occurs as part of a traumatic event, such as injury or disease. For example, a patient's nociceptive pain in response to noxious stimulation may be accompanied by feelings of annoyance, fear, distress, and/or suffering. Accordingly, patients experiencing the same level of nociceptive pain may describe that pain differently, resulting in different diagnoses and treatments. Those problems are exacerkated when the patient cannot provide a description of their pain and the healthcare provider must rely solely on his or her own physical observations of the patient, such as with young children, infants, neonates, non-verbal patients, and patients with developmental disabilities.
The nociceptive component of pain may also be subjective to specific patients. For example, a patient may experience an exaggerated reaction to nociceptive pain if he or she is suffering from hyperalgesia. A patient may experience an increased sensitivity to nociceptive pain as part of sickness behavior (i.e., the evolved response to illness). And a patient may experience nociceptive pain from stimulus that does not normally provoke such pain if he or she is suffering from allodynia. Accordingly, some patients may be more sensitive to pain than others and, therefore, may experience nociceptive pain out of proportion to physical findings, making it particularly difficult to properly diagnose and treat those patients.
In addition to the different subjective components of pain experienced by a patient, a patient may also inadvertently attempt to sabotage the assessment of his or her pain. For example, the patient may be unwilling to communicate the extent of his pain or fear that he or she will be seen by the healthcare provider as a bother or drug seeker. Or the patient's attitude toward his or her ailment may be depressed and fatalistic, causing him or her to feel that the pain is inevitable and must be tolerated. Some healthcare providers may even adopt an attitude that pain is inevitable and must be tolerated or allow personal prejudice or bias to interfere with the independence of their assessment. Thus, there are many subjective factors—both internal and external to a patient—that can potentially bias pain assessment, thereby resulting in inaccurate diagnoses and ineffective, inadequate, and/or excessive treatments.
Those subjective factors not only negatively affect the diagnosis and treatment of pain, they also negatively affect clinical trials on the efficacy of drugs used in the management of pain (i.e., analgesics and other pain interventions). The main outcome variables in such clinical trials are pain relief and pain reduction. But because of the highly interindividual variability of the results obtained with conventional pain assessment apparatus/methods, it is difficult to obtain an objective measure of pain relief and pain reduction (i.e., efficacy) in clinical trials or other clinical evaluations. Thus, the results of those clinical trials are limited in their accuracy and, therefore, usefulness.
Not only is it difficult to objectively measure the efficacy of analgesics with conventional pain assessment apparatus/methods, long-term and/or high dose use of certain analgesics may exacerbate that difficulty. For example, long-term and/or high-dose use of opioids (e.g. morphine, heroin, hydrocodone, oxycodone, and methadone) may result in a patient developing an increased sensitivity to noxious stimuli (i.e., opioid-induced hyperalgesia) and/or evolving a painful response to previously non-noxious stimuli (i.e., opioid-induced allodynia). However, those forms of opioid-induced toxicity present a similar net effect as tolerance to opioids, making them difficult to distinguish from tolerance in a clinical setting. And while increasing the dose of an opioid can be an effective way to overcome tolerance, doing so to compensate for opioid-induced hyperalgesia or allodynia may paradoxically worsen the patient's condition by increasing sensitivity to pain while escalating physical dependence. In such cases, the patient may actually benefit from complete withdrawal of opioid treatment. Therefore, it is of the utmost importance for healthcare providers to be able to diagnose, quantify, and distinguish actual pain from treatment-induced side effects. In addition, it is of a great deal of importance for healthcare providers to be able to identify the development of such forms of opioid-induced toxicity so they can be distinguished from tolerance and the appropriate therapy can be instituted.
As set forth above, there is a need in the art for an apparatus and method for objectively and quantitatively assessing and characterizing pain in patients—particularly, in young children, infants, neonates, and non-verbal patients or otherwise verbally or cognitively challenged patients, such as patients with developmental disabilities. There is also a need in the art for an apparatus and method for objectively measuring the effect of currently used analgesics and other pain interventions, and to objectively measure the efficacy and dose-response relationships of newly developed and/or investigational drugs and interventions targeted for pain management. And there is a need in the art for an apparatus and method for detecting the onset of tolerance and/or analgesic-induced toxicity to such analgesics. Moreover, multiple lines of evidence suggest that repeated and prolonged pain exposure in neonates, at a time when it is developmentally unexpected, alters their subsequent pain processing, long-term development, and behavior. Therefore, the proper diagnosis, quantification of pain, and appropriate pain therapy during the neonatal period is of utmost importance to prevent such alterations in pain processing pathways after the neonatal period.